Inhibition of 141B decomposition

ABSTRACT

Inhibition of the formation of unsaturated carbon compounds during the heating of 141b involving the addition of various inhibitors such as butylene oxide and/or the use of a vessel made of a nickel alloy.

This is a continuation of application Ser. No. 08/119,905 filed Sep. 10,1993, U.S. Pat. No. 5,531,867, which was a continuation of applicationSer. No. 07/983,919 filed Dec. 1, 1992, abandoned, which was acontinuation-in-part of application Ser. No. 07/869,225 filed Apr. 14,1992, abandoned.

FIELD OF THE INVENTION

The present invention relates to a method of inhibiting the formation ofunsaturated carbon compounds and other unwanted by-products formedduring she heating of 1,1-dichloro-1-fluoroethane ("141b"), especiallyas it relates to the separation of 141b from a liquid mixture containing1,1,1,2-tetrachloroethane ("130a") and, if present,1,1,1-trichloroethane ("140a") via distillation.

BACKGROUND OF THE INVENTION

The hydrochlorofluorocarbon 141b is a replacement fortrichlorofluoromethane ("11") as a foam blowing agent. As shown byBrooks et al. in U.S. Pat. No. 4,948,479 (the entire specification ofwhich is hereby incorporated by reference), however, the manufacture of141b from 140a and hydrogen fluoride ("HF") results in the formation ofvinylidene chloride ("1130a") and other unsaturated by-products andacids, principally HCl. Because of similar boiling points, 141b (b.p.32° C.) and 1130a (b.p. 31° C.) cannot be readily separated bydistillation. Thus, Brooks et al. teach the use of a photochlorinationstep to convert the 1130a in the 141b product stream to the higherboiling 130a (b.p. 130.5° C.), then distillation of the photochlorinatedliquid mixture to separate the low boiling 141b from the higher boilingliquids such as 130a (and possibly 140a unless it has been removedupstream). However, it is found that 1130a and acid (primarily HCl withlesser amounds of HF) are reformed in the distillation column anddistill overhead with the 141b product. While the acid can be removedfrom the product by selective adsorption or reaction, such as by passingthe acidic 141b through a bed of potassium hydroxide, it is undesirablesince it is an added step. Reformation of the 1130a is more difficult,however, because as noted above it has nearly the same boiling point asthe desired 141b product. Thus, yet another post-treatment would berequired to remove the 1130a unless its formation in the distillationcolumn can be inhibited. The same problem is presented when 141b isformed by the reaction of 1130a and HF [as taught, for example, by Henneet al., JACS 65, 1271 (1943)], resulting in a product stream containing141b and 1130a.

SUMMARY OF THE INVENTION

A method is provided for inhibiting the formation of unsaturated carboncompounds during the heating of 141b (alone or as a liquid mixturecontaining 130a or both 130a and 140a), which method comprisesconducting said heating (a) in the presence of an effective amount of aninhibitor selected from a dialkylhydroxylamine where the alkyl groupshave 1 to 4 carbons such as methyl, ethyl, propyl, or butyl [preferablydiethylhydroxylamine ("DEHA")]; an epoxide (or cyclic oxide) having 3 to6 or 10 to 30 carbons such as alpha-pinene oxide ("APO"), 1,2-hexadeceneoxide ("HO"), butylene oxide ("BO"), limonene monoxide, limonenedioxide, methyl epoxy soyate, propylene oxide, dicyclopentadiene dioxidealcohol, isoprene oxide, glycidyl isopropyl ether, 1,4-dioxane, or anepoxidized alpha olefin such as C₁₀ H₂₀ O, C₁₂ H₂₄ O, or C₁₆ H₃₂ O(preferably APO, HO, or BO); a free radical scavenger having at leasttwo double bonds and a boiling point greater than that of 141b such asalpha-methyl-styrene ("AMS"), limonene or one of its optical isomerssuch as d-limonene ("DL"), alloocimene, or isoprene (preferably AMS orDL); a phenol, the phenyl group of which can be unsubstituted orsubstituted at one or more of the ring positions with substituentsseparately selected from alkyl (such as methyl, ethyl, isopropyl,butyl), alkoxy (such as methoxy, ethoxy, propoxy, isopropoxy), nitro,halo (such as F, Cl, or Br), alkylamine salt (such as --N(CH₃)₃ ⁺ Cl⁻),acyl (--C(O)R where R is alkyl), acyloxy (--OC(O)R where R is alkyl),cyano, hydroxy, phenyl which is unsubstituted or substituted as above,the alkyl portion of such substituents generally being lower alkyl of 1to 4 carbons, and wherein two adjacent positions of the phenyl group canhave substituents which are Joined to form a fused aromatic ring as innaphthol (preferred phenols being 2,6-di-t-butyl-4-methylphenol and4-methoxyphenol); or a 1,4-benzoquinone which can be unsubstituted orsubstituted at each of the aromatic ring positions with substituentsseparately selected from those listed for phenol (the preferredbenzoquinone being unsubstituted); or (b) in a vessel made of a nickelalloy.

This method is particularly applicable to separation of 141b from aliquid mixture containing 130a (and, optionally, 140a) in a distillationcolumn. If an inhibitor is used, it is added to the bottom (or"reboiler" section) of the column. If the column is made of a nickelalloy, use of an inhibitor is not necessary.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the invention it has now been found that thepresence of the aforementioned inhibitors inhibits the formation ofunsaturated carbon compounds such as 1130a and acids such as HCl and HFduring the heating of 141b, such as occurs when a liquid mixturecomprising 141b, 130a, and, optionally, 140a is heated in a distillationcolumn to separate low boiling compounds such as 141b from higherboiling compounds such as 130a (and 140a, if present).

When added to a distillation column, the inhibitor should be added tothe bottom or reboiler section of the column where the temperature ishighest, typically on the order of from about 75° F. to about 200° F.(preferably about 90°-160° F.). The temperature at the top of the columnis typically about 20 degrees lower than that at the bottom. Adding theinhibitor to the feed stream to the column, as opposed to the columnbottom, has been found to be ineffective.

The inhibitor is generally fed to the column at a rate sufficient tomaintain a level of inhibitor in the bottoms stream exiting the columnof from about 500 to about 5000 ppm, more typically from about 1500 toabout 3500 ppm.

This embodiment is illustrated in Examples 1-5 below (where percents areweight percent unless otherwise noted). Examples 1-3 employ aconventional carbon steel column.

In a second embodiment it has now been found that the use of nickelalloys such as Nickel, Monel, Inconel, Hastelloy, or Carpenter 20 forthe vessel in which the heating or distillation is conducted iseffective to inhibit the formation of acids and 1130a without the use ofinhibitors. Inconel and Hastelloy alloys are particularly preferred.Exclusion of air from such processes also assists in the inhibition.This embodiment is illustrated by Example 5 and 6.

Example 1--A crude, photochlorinated mixture, produced according to themethods of the Brooks et al. patent and containing about 100 ppm of1130a and, as the other major components, about 98% 141b, 1.5% 140a, and0.3% 130a, was distilled in a steam-heated column which was operated ana temperature at the column top of about 120° F., a temperature at thecolumn bottom of about 140° F., and a pressure of about 15 PSIG. The141b taken overhead typically showed the formation of 300 to 600 ppm of1130a and over 20 ppm acidity (calculated as HCl).

Example 2--Example 1 was repeated except that butylene oxide was fed toreboiler section of the column at a rate sufficient to maintain a levelof 2500 ppm of the butylene oxide in the bottoms stream. There was nodetectable formation of 1130a or acid as a result of the distillation.

Example 3--Examples 1 and 2 were repeated except that the 140a level inthe feedstream was reduced to about 50 ppm. Distillation as in Example iresulted in the formation of about 170 ppm of 1130a and over 10 ppmacidity. With the use of butylene oxide as in Example 2, distillationresulted in the formation of only about 30 ppm of 1130 and about 1 ppmof acidity.

Example 4:

A) A mixture containing as major components about 84.1% 141b, 0.2% 130a,and 15.3% 140a was tested to compare the ability of various inhibitorsto prevent the formation of acidity (the starting mixture contained 5.3ppm acid as HCl). Samples containing 2000 ppm of inhibitor (except inthe control with no inhibitor) were placed in glass bottles and set oneinch from a 450-watt UV lamp for 5 hours. With no inhibitor (thecontrol) over 120 ppm of acidity resulted. With six inhibitors of thisinvention (DEHA, APO, HO, BO, AMS, and DE) less than 10 ppm of acidityresulted.

B) The above test was repeated except that the samples were placed inmild steel cylinders and heated at 100 degrees Centigrade for 7 hours.With no inhibitor (the control) over 170 ppm of acidity resulted. Withnine inhibitors of this invention (DEHA, APO, HO, BO, AMS, DL,benzoquinone, 4-methoxyphenol, and 2,6-di-t-butyl-4-methylphenol) lessthan 10 ppm of acidity again resulted.

Example 5--Crude, 141b-containing, column bottom material was heated incylinders made of different metals and analyzed. A 316 Stainless Steelcontainer heated to 180° F. for 16.5 hours showed a 5-fold increase in1130a, while the same container heated to 252° F. for 23 hours showed noincrease in 1130a when 1800 ppm of butylene oxide inhibitor was added.Mild steel containers heated to 257° F. for 4 hours showed a 340 ppmincrease in 1130a with no inhibitor, but only a 50 ppm increase in 1130awhen 1600 ppm of butylene oxide inhibitor was added. When Monel (analloy containing 63-70% by weight nickel) was heated to 257° F. for 4hours, no increase in 1130a occurred even though no inhibitor waspresent.

Example 6--Relatively pure 141b samples (99.3% 141b) without inhibitorwere placed in glass tubes containing small coupons of various metalsand heated for 2 hours at 356° F. The mild and stainless steels resultedin the formation of.495-1755 ppm of 1130a, while Inconel 600 (an alloycontaining 72% nickel) and Hastelloy C-276 (an alloy containing about60% nickel) resulted in no 1130a formation, Nickel (99-100% nickel)resulted in 250 ppm of 1130a, Monel 400 (63-70% nickel) resulting in 335ppm of 1130a, and Carpenter 20 (an alloy containing 32-38% nickel)resulted in 450 ppm of 1130a.

What is claimed is:
 1. A method for inhibiting the formation ofby-products during the heating of 1,1-dichloro-1-fluoroethane, whichmethod comprises heating 1,1-dichloro-1-fluoroethane in a distillationcolumn made of a nickel alloy.
 2. A method as in claim 1 wherein thealloy is an Inconel 600 or Hastelloy alloy.
 3. A method as in claim 2wherein the alloy is Inconel
 600. 4. In a process for separating1,1-dichloro-1-fluoroethane from a liquid mixture containing1,1,1,2-tetrachloroethane in a distillation column, the improvementwhich comprises making said column out of a nickel alloy so as toinhibit the formation of by-products.
 5. A process as in claim 4 whereinthe alloy is an Inconel 600 or Hastelloy alloy.
 6. A process as in claim5 wherein the alloy is Inconel 600.